From the perspective of the radio network side, there are two states, i.e., the RRC_connected state and the RRC_idle state, of a UE in a Long Term Evolution (LTE) system; and there are five states, i.e., cell_dch, cell_fach, cell_pch/ura_pch, and idle states, of a UE in a Universal Mobile Telecommunication System (UMTS), where cell_dch, cell_fach and cell_pch/ura_pch belong to the RRC_connected state. Only the UE in the RRC_connected state can transmit uplink data. Once the UE transmits all of uplink data, the network side releases the Radio Resource Control (RRC) connection of the UE in an RRC Connection Release message upon detecting that the UE has no data transmitted for a long period of time, so that the UE enters the RRC_idle state.
The UE in the idle state primarily operates to monitor paging from the network side. In order to save power, the UE generally monitors paging in a Discontinuous Reception (DRX) mode in which the UE receives only for a short period of time in each cycle but does not receive in the remaining period of time in the cycle, as illustrated in FIG. 1. In the UMTS system, the length of time of a DRX cycle configured at the network side at present is at most 29 radio frames (i.e. 5120 ms), that is, from the perspective of DRX in the UMTS system, the UE enables a receiver at most once every 5120 ms to receive a paging instruction message, and possibly a paging message, from the network side, but disables the receiver in the remaining period of time. The longest DRX cycle configured at the network side at present in the LTE system is 2560 ms.
There are possibly two DRX cycle lengths configured for the UE in both the UMTS system and the LTE system. One is configured by a Radio Network Controller (RNC)/evolved Node B (eNB) in a System Information Block (SIB) message and can be referred to a default DRX, which is applicable to all of UEs residing in the cell; and the other DRX is negotiated about by a Core Network (CN) entity and the UE in a Non-Access Stratum (NAS) procedure and can be referred to a UE specific DRX, which is only applicable to a single UE. The latter DRX length is unknown to the RNC/eNB in the negotiation procedure of the CN entity and the UE. The UE monitors a paging message at the shorter one of the two DRX cycles.
The paging procedure is initiated by the CN entity firstly transmitting the paging message to the RNC (UMTS)/eNB (LTE). The paging message is transmitted by a Mobility Management Entity (MME) to the eNB via an S1 interface in the LTE system, as illustrated in FIG. 2; and transmitted via an Iu interface in the UMTS system, as illustrated in FIG. 3. If the paging message carries the UE specific DRX configuration, then the RNC will transmit the paging message via the air interface using a DRX parameter configured in the paging message in the UMTS system. The eNB will compare the DRX parameter in the DRX configuration with a DRX parameter configured in a system message and transmit the paging message at the shorter one of the DRX cycles in the LTE system.
Calculation of a occasion at which the UE receives paging is related directly to a System Frame Number (SFN) and an International Mobile Subscriber Identity (IMSI). Particularly a occasion at which the UE receives paging can be calculated as specified in the 3GPP TS 36.304 protocol in the LTE system; and a occasion at which the UE receives paging can be calculated as specified in the 3GPP TS 25.304 protocol in the UMTS system.
Machine-Type Communication (MTC), which is a new communication idea, is intended to integrate a number of different types of communication technologies together, e.g., machine-to-machine communication, machine controlled communication, human-to-machine interactive communication, mobile Internet communication, etc., to thereby develop social production and life styles. As expected, human-to-human communication services will account for only one third of the UE markets in the future, whereas a larger amount of communication will emerge as MTC communication services. Sometimes MTC communication is also referred to as Machine-to-Machine (M2M) communication or the Internet of Things.
An important issue of power saving needs to be considered in an MTC communication scenario. In some scenarios, the lifetime of an MTC device is determined directly by the lifetime of a battery, for example, an MTC device for tracking an animal or an MTC device for hydrologic supervision, for both of which it is nearly impossible to replace their batteries, so the MTC device is required to consume an extremely low amount of power. A longer DRX cycle needs to be applied to the MTC device for more power saving. Thus the DRX cycle specified in the existing protocols (2.56 seconds in the LTE system, and 5.12 seconds in the UMTS system) needs to be extended to an order of a minute and even an hour.
However if the UE monitors in the extended DRX cycle, then some problem may occur, for example, there may be a longer delay in receiving paging due to a longer interval of time between two paging occasions; and in another example, if some paging initiated by the network side is not received by the UE due to a limited resource, a poor channel quality, or another reason, then the UE has to wait for a longer period of time (which is the extended DRX cycle) to receive next paging, thus degrading the reliability of receiving the paging.
In summary, if the UE monitors in the extended DRX cycle in the prior art, then there may be a longer delay in receiving paging, and degraded reliability of receiving the paging.